Transparent glowing material
For Cycles render engine, a possible node set up could be this:



With the Texture coordinate node's Object output we are gathering the information about where to place the following texture. Object will use the object's origin, rotation and scale, so the texture will be placed in the middle of the plane.

The following node, Vector Mapping, is tweaking a bit the scale of the texture upon the Z axis, as we are going to use a spherical gradient, while what we need is more like a half ellipsoid.

First Color Ramp is needed to adjust the feather of the texture border, second Color Ramp gives the shades of color to the emission node.

Last step is to mask out the emission shader using the first Color Ramp node output as the mixing factor fwith a transparent shader (don't forget to increase the trasparency bouces to at least the number of planes in the array)

Note: to increase the realism, I suggest to work upon the emission intensity rather than the color: